X-ray tube



, June 25, 1957 co E ET AL 2,797,350

X-RAY TUBE Filed Nov, 27 1 953 YINVENTORSI BART COM JACOBUS MARIN TMANV y Y. I I

X-RAY TUBE Bart Combe and Jacobus Marinus Houtman, Eind-hoven, Netherlands, assignors, by mesne assignments, to North American Philips Company, Inc., New York, N. Y., a corporation of Delaware Application November 27, 1%3, Serial No. 394,816

Claims priority, application Netherlands December 1, 1952 4 Claims. (Cl. $13-$30) In many kinds of X-ray tubes, use is made of an anode which is made from copper and of which the electron target, which consists of tungsten, is in good heat-conductive contact with the copper. When the X-ray tube is loaded, a strong development of heat occurs in the target, a large proportion of which with increasing temperature of the target is dissipated to the copper body and then transferred to a cooling agent and carried off. As a rule, the amount of heat being supplied is larger than that which is carried off by the cooling agent during the same period, so that the temperature continuously increases, and the duration of the load is limited by the highest permissible temperature that can be tolerated.

The thermal contact between the tungsten target and the copper body constitutes an important factor for the distribution of temperature in the anode. If the condition of an optimum thermal contact is not fulfilled, a smaller amount of heat is dissipated from the target and the load on the X-ray tube is required to be made lower. With unvaried load the target is unduly heated and either the material is liable to be evaporated or the tube becomes unserviceable due to flaws occurring in the target.

An important disadvantage in such X-ray tubes results from the fact that the thermal contact which is initially satisfactory can become poorer after the tube has been in use for a longer or shorter period. The quickly-varying important temperature variations resulting from the anode material being loaded to the highest permissible temperature and subsequently cooled are responsible for the high stress in the material which occurs at the boundary between the two materials. During the investigation in regard to the kind of the damage involved it has been found that the adherence between the copper and the target is substantially all right, but flaws in the copper are present.

In certain cases steps have been taken with the purpose to obviate the said disadvantage. One of these steps is to allow the growth of large crystals behind the target. An improvement could also be obtained by strengthening the copper, for which purpose a metal wool plug of a 'metal having a greater strength than copper, preferably of tungsten, was sealed directly behind the target. It has been possible in this way to obtain a satisfactory period of life considering the number of loads that the X-ray tube can endure. However, the continuous extension of medical investigations with X-rays has the consequence that the period of time in which the X-ray tube has undergone the average number of loads is comparatively short, so that actually the tube requires to be replaced too soon. Probably the short intervals between the loads also have an unfavourable effect upon the life of the tube.

Another reason for the X-ray tube becoming unserviceable, which occurs when the period of life is lengthened, is the occurrence of recrystallisation of the copper at areas which, as regards the dissipation of heat, are gated in a so-called dead angle. Since the material soice to-say pulverises as a result of recrystallisation, its conductivity of heat decreases, while metal particles readily become detached from the surface if the said phenomenon occurs superficially.

The object of the invention is further to increase the average number of loads which X-ray tubes of this kind can endure and to make possible the manufacture of X-ray tubes which no longer become unserviceable primarily as a result of a decreased thermal contact between the copper body and the tungsten target. According to the invention, a copper anode for X-ray tubes comprises an electron target of tungsten constituted by a small plate of which two opposite sides are bent rectangularly or substantially rectangularly to the same side, the plate except the target area for the electrons being wholly embedded in the copper.

Such an anode is probably indebted for its greater strength to the fact that the copper located behind the target is enclosed between the upright edges of the target which are penetrated into the metal. The movability of the copper crystals may be further decreased and the particles may be mutually anchored by sealing in known manner a plug of metal wool directly behind the tungsten plate.

In an improved form of an anode according to the invention it is ensured that the surface of that metal of the anode which embraces the target adjoins the bent edges thereof at substantially right angles.

In order that the invention may be readily carried into effect, it will now be described with reference to the accompanying drawing showing, by way of example, in Fig. l and Fig. 2, two embodiments thereof. Furthermore, the provision of the metal wool is shown.

The anode is constituted by the copper body 1 of cylindrical shape which has a large volume in proportion to the tungsten target 2 in order to fulfil its function as a heat-sink. The target is made as small as possible in order that the path which must be traversed by the heat developed therein may be as short as possible. Since the thermal conductivity of copper is materially greater than that of tungsten, the dissipation of heat takes place more rapidly if the path to be traversed in the tungsten is shorter. A long anode is also unfavorable to arrive at great uniformity in the distribution of heat as is aimed at in order to make the temperature dilferences in the anode not greater than necessary, so that the diameter of the anode, as a rule, considerably exceeds the size of the target for the electrons. 3 and 4 indicate the edges of the tungsten plate which are bent backwards, furnishing a generally U-shaped member, and which edges are wholly embedded in the copper, thus enclosing the copper located in between. 5 indicates the plug of metal wool which is likewise provided within that portion of the anode which is bounded by the bent edges or arms of the U-shaped target 2.

The heat produced in the target 2 expands in all directions. The range of the highest temperature is located between the outer paths of the beam of electrons striking the exposed surface of the bight portion of the U-shaped target. Said paths are indicated in dotted line by 6 and 7. However, since the boundaries of the said range approach the edges of the target, the heat which is dissipated in directions parallel to the surface is liable to cause detrimental recrystallisation of that material of the anode which adjoins the bent edges of the target. The material concerned is located in a so-called dead angle in which heat is accumulated more or less due to the cross-section for the dissipation of the heat becoming narrower towards the target. In order to obviate the aforementioned risk, in the construction shown in Fig. 2 the anode material is removed from the said areas, which are indicated by 8 and 9 on each side of the target, so that the surface ad! joins the side-walls of the bent edges of the target at substantially right angles.

What is claimed is:

p 1. An anode for an X-ray tube comprising a copper, body, a U-shaped tungsten target plate whollyiembedded.

in said coppertbodywith the arms of the U being substantially perpendicular to the bight and facinginwardly into the copper body and theouter-surface of'the bight of the U being exposedfor receiving electrons and being substantially flush with the outer-surfaceof the copper, and a tungsten wool plug sealed in the copper body be tween the arms of the U.

2; An anode as claimed in claim 1' in whichtheisurface of the copper body adjacent the arms of the. U. adjoins therewithsubstantially at right angles.

3. An anode for an X-ray-tube comprising acopper body having a givenwidth, and a tungsten target having a generally U-shaped cross-section and constituted of .a single body having arm portions extending substantially perpendicular from a common bight portion, said arm portions having a width less than said given width of the copper body, said target being embedded substantially centrally in said copper body with the arm portions facing in toward the copper body and with the outer surface of the bight portion exposed and lying substantially in a common plane with the adjacent surfaces of the copper body, said arm portions lying wholly within the copper body.

4. An anode as claimed in claim 3 wherein the copper body has small recessestherein adjacent the embedded arm portions of the target.

References Cited in the file of this patent UNITED STATES PATENTS 1,218,026 Wiggin Mar. 6, 1917 1,279,423 Pfanstiehl Sept. 17, 1918 1,893,759 Bouwers Ian. 10, 1933 2,125,896 Driggs et a1. Aug. 9, 1938 2,311,725 Atlee Feb; 23, 1943 2,490,246 Zunick Dec. 6, 1949 

1. AN ANODE FOR AN X-RAY TUBE COMPRISING A COPPER BODY, A U-SHAPED TUNGSTEN TARGET PLATE WHOLLY EMBEDED IN SAID COPPER BODY WITH THE ARMS OF THE U BEING SUBSTANTIALLY PERPENDICULAR TO THE BIGHT AND FACING INWARDLY INTO THE COPPER BODY AND THE OUTER SURFACE OF THE BIGHT OF THE U BEING EXPOSED FOR RECEIVING ELECTRONS AND BEING SUBSTANTIALLY FLUSH WITH THE OUTER SURFACE OF THE COPPER, AND A TUNGSTEN WOOL PLUG SEALED IN THE COPPER BODY BETWEEN THE ARMS OF THE U. 